Am 2022-04-30 21:33, schrieb Clint Jay:
I think the reason the PICDiv is so well regarded is because of the
specific chips used and the way the timers etc. are implemented in
them.
So, an alternate chip outside of the Microchip PIC range just might not
be
capable of the performance.
For me, the alternate chip is a Xilinx Coolrunner II with the following
half page of VHDL code. For my board, there is also a phase comparator
on the chip, options for different OCXOs / more frequencies and space
for syncing an OCXO to an incoming 1 pps (not tested).
Just 1 pps generation should fit into an X2C32 (i.e. half the size), to
200 MHz.
Pulse precision is like a 74LVC flip flop.
Cheers, Gerhard
----------------------------------------------------------------------------------
-- Company: Hoffmann RF & DSP
-- Create Date: 09:09:37 08/08/2012
-- Module Name: ppps1_generator - Behavioral
-- Target Devices: X2c64A-5VQ44
-- Additional Comments: Free firmware under BSD license
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use ieee.numeric_std.all;
entity pps1_generator is
Port(
clk : in STD_LOGIC;
RunAt100MHz : in STD_LOGIC;
pps1_out : out STD_LOGIC;
);
end pps1_generator;
architecture Behavioral of pps1_generator is
signal tctr : integer range 0 to 99999999;
signal pw_ctr : integer range 0 to 199999;
signal cycle_done : boolean;
signal pw_done : boolean;
function bool2sl(b : boolean) return std_logic is
begin
if b then
return '1';
else
return '0';
end if;
end function bool2sl;
begin
u_div: process(clk) is
begin
if rising_edge(clk) then
cycle_done <= (tctr = 0); -- pipeline the comparator
if cycle_done
then
if RunAt100MHz = '1' then -- reload
tctr <= 100000000 - 2; -- divide by 100
Meg
else
tctr <= 10000000 - 2; -- divide by 10
Meg
end if;
else
tctr <= tctr - 1;
end if;
end if; -- rising_edge()
end process u_div;
-- produce the standard 20 usec pulsewidth
u_pulsewidth : process(clk) is
begin
if rising_edge(clk) then
if cycle_done then
if RunAt100MHz = '1' then
pw_ctr <= 19999;
else
pw_ctr <= 1999;
end if;
elsif pw_ctr /= 0 then
pw_ctr <= pw_ctr - 1;
end if;
pps1_out <= bool2sl(pw_ctr /= 0);
end if; -- rising_edge()
end process u_pulsewidth;
end Behavioral;
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